Fix compiler warnings

lib/blisp.c

@@ -73,7 +73,7 @@ int32_t blisp_device_open(struct blisp_device* device, const char* port_name) {
   sp_set_stopbits(serial_port, 1);
   sp_set_flowcontrol(serial_port, SP_FLOWCONTROL_NONE);
 
-  uint32_t vid, pid;
+  int vid, pid;
   sp_get_port_usb_vid_pid(serial_port, &vid, &pid);
   device->is_usb = pid == 0xFFFF;
   //  if (device->is_usb) {

lib/blisp_easy.c

@@ -24,6 +24,8 @@ static int64_t blisp_easy_transport_size(struct blisp_easy_transport* transport)
     return transport->data.memory.data_size;
   } else {
     // TODO: Implement
+	  printf("%s() Warning: calling non-implemented function\n", __func__);
+	  return -1;
   }
 }